• Journal of the Korean Society of Combustion
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• v.14 no.4
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• pp.48-53
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• 2009

This paper describes the forced flame response in a turbulent premixed gas turbine combustor. The fuel was premixed with the air upstream of a choked inlet to avoid equivalence ratio fluctuations. To impose the inlet flow velocity, a siren type modulation device was developed using an AC motor, rotating and static plates. Measurements were made of the velocity fluctuation in the nozzle using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The test results showed that flame length as well as geometry was strongly dependent upon modulation frequency in addition to operating conditions such as inlet velocity. Convection delay time between the velocity perturbation and heat release fluctuations was calculated using phase information of the transfer function, which agreed well with the results of flame length measurements. Also, basic characteristics of the flame nonlinear response shown in the current test conditions were introduced.

• JSTS:Journal of Semiconductor Technology and Science
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• v.5 no.3
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• pp.187-194
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• 2005

An analysis of the 1/f or flicker noise in FD n-channel Double Gate SOI MOSFET is proposed. In this paper, the variation of power spectral density (PSD) of the equivalent noise voltage and noise current with respect to frequency, channel length and gate-to-source voltage at various temperatures and exponent $C(i.e\;1/f^c$ is reported. The temperature is varied 125 K from to room temperature. The variation of PSD with respect to channel length down to $0.1{\mu}m$ technology is considered. It is analyzed that l/f noise in FD n-channel Double Gate SOI MOSFET is due to both carrierdensity fluctuations and mobility-fluctuations. But controversy still exits to its origin.

• Journal of The Korean Astronomical Society
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• v.45 no.1
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• pp.19-24
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• 2012

Microthermal fluctuations are introduced by atmospheric turbulence very near the ground. In order to detect microthermal fluctuations at Fuxian Solar Observatory (FSO), a microthermal instrument has been developed. The microthermal instrument consists of a microthermal sensor, which is based on a Wheatstone bridge circuit and uses fine tungsten filaments as resistance temperature detectors, an associated signal processing unit, and a data collection, & communication subsystem. In this paper, after a brief introduction to surface layer seeing, we discuss the instrumentation behind the microthermal detector we have developed and then present the results obtained. The results of the evaluation indicate that the effect of the turbulent surface boundary layer to astronomical seeing would become sufficiently small when installing a telescope at a height of 16m or higher from the ground at FSO.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.51.1-51.1
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• 2016

Turbulent motions produce density and magnetic field fluctuations. Correlation between density and magnetic field fluctuations are important for interpretation of observations, such as the rotation measure (RM) and dispersion measure (DM). We study the several factors that can affect the correlation between two. In particular, we numerically investigate how the correlation time of driving affects the correlation between density and magnetic field. We perform compressible MHD turbulence simulations at different sonic Mach number and consider two different driving schemes - continuously changing driving and delta-correlated driving. The continuously changing driving results in strong anti-correlation between density and magnetic field when sonic and Alfvenic Mach numbers are similar unity. The delta-correlated driving produces virtually no correlation between two fields.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2010.05b
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• pp.103-108
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• 2010

The purpose of this study is to analyze of the risk factors for oversea plants construction projects. For this study, risk factors data from related literature review, research organization and construction company was researched and classified under each EPC phases. In addition, a questionnaire survey by plant experts was conducted for analysis of risk weight and costs and time impact on each EPC phases. The results of this study are as follows: First, a detail design errors(engineering phase), a equipment procurement plan(procurement phase), and exchange rate fluctuations(construction phase) were analyzed the highest weight factors. Second, a financing plan(engineering phase), quantity take-off bill(procurement phase), and exchange rate fluctuations(construction phase) were analyzed the highest cost impact factors. Third, detail design errors(engineering phase), a equipment procurement plan(procurement phase), and schedule management errors(construction phase) were analyzed the highest time impact factors.

• ETRI Journal
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• v.16 no.2
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• pp.1-13
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• 1994

We have identified two new features related to the coherent transport in the mesoscopic loop structure of aluminum wire, including the autocorrelation of the conductance fluctuations beyond $B_c$ and fine structure in the low-field magnetoresistance curve in the superconducting transition regime, which, to the best of our knowledge, have not been reported in the literature. Since the electrons in Al have a phase coherence length larger than $1\;{\mu}m$ at or below T = 3K, which is comparable to the dimensions of the structure, the wave nature of the electronic transport has been clearly observed: the universal conductance fluctuations, the Aharonov-Bohm oscillations, and the Altshuler-Aronov-Spivak oscillations. Due to the transition of Al to a superconducting state at T = 1.3 K, the coherent phenomena of Cooper pairs, i.e., the Little-Parks oscillations, have also been observed.

• Advances in aircraft and spacecraft science
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• v.1 no.4
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• pp.443-454
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• 2014

An experimental study was conducted to investigate the effect of Reynolds number on compressible convex-corner flows, which correspond to an upper surface of a deflected flap of an aircraft wing. The flow is naturally developed along a flat plate with two different lengths, resulting in different incoming boundary layer thicknesses or Reynolds numbers. It is found that boundary layer Reynolds number, ranging from $8.04{\times}10^4$ to $1.63{\times}10^5$, has a minor influence on flow expansion and compression near the corner apex in the transonic flow regime, but not for the subsonic expansion flow. For shock-induced separated flow, higher peak pressure fluctuations are observed at smaller Reynolds number, corresponding to the excursion phenomena and the shorter region of shock-induced boundary layer separation. An explicit correlation of separation length with deflection angle is also presented.

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1246-1257
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• 2004

The objective of this paper is to characterize dynamic pressure traces measured at self-excited combustion instabilities occurring in two combustion systems of different hardware. One system is a model lean premixed gas turbine combustor and the other a fullscale bipropellant liquid rocket thrust chamber. It is commonly observed in both systems that low frequency waves at around 300㎐ are first excited at the onset of combustion instabilities and after a short duration, the instability mode becomes coupled to the resonant acoustic modes of the combustion chamber, the first longitudinal mode for the lean premixed combustor and the first tangential mode for the rocket thrust chamber. Low frequency waves seem to get excited at first since flame shows the higher heat release response on the lower frequency perturbations with the smaller phase differences between heat release and pressure fluctuations. Nonlinear time series analysis of pressure traces reveals that even stable combustion might have chaotic behavior with the positive maximum Lyapunov exponent. Also, pressure fluctuations under combustion instabilities reach a limit cycle or quasi-periodic oscillations at the very similar run conditions, which manifest that a self-excited high frequency instability has strong nonlinear characteristics.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.5
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• pp.113-118
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• 2017

In this paper, we propose a design procedure for determining the gate position robust to changes and inherent fluctuations in the process conditions during injection molding. To evaluate the robustness of the gate position, the signal-to-noise ratio is used, and noise conditions are implemented using orthogonal arrays, where the process variables are considered as noise factors and possible process fluctuations are set as the levels of the noise factors. To show the usefulness of the proposed robust design procedure, we apply it to a computer CPU baseplate. As a result, it is shown that a robust gate position can be determined that reduces the average warpage deflection by 2.4% and 1.7%, and the variance by 3.4% and 5.1%, compared to the two initial gate positions.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.3
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• pp.342-348
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• 2013

As a number of wind power generation systems have been installed in power systems in the world, frequency fluctuations due to output power variations from wind farms have become a serious problem. Battery systems have been studied for smoothing the output variations and decreasing the resulting frequency fluctuations. Among these studies, efficient design of battery systems is one of the most important subjects from a point of view of cost. This paper presents a comparative analysis of the smoothing effect between the conventional moving average method and a new method based on frequency response analysis.